Posts and images: removing old versions of post

I would like to delete images that i am not using from my media library.

I am having some problems in doing it, because i have images that appear linked to a post, when i am not displaying them in the final version of that post!
Maybe it's beacuse i attachee it to that post, in a previuos version of that post.
So, how can i delete previous version of my post? (My post are public)

a) Yes, any photo you uploaded via the Add Media tool of a post will appear as attached to that post, even if you never inserted it into the post or if you inserted it then deleted it. If you're sure which these images are, you can delete them.

b) But since you've only used 10% of the available storage space, you needn't really bother.

c) What you need to do is avoid wasting your storage space like you've being doing. (To give you a counter example, in my tests blog I have uploaded more than a thousand images so far, and they've only taken up 8% of the space). Don't upload the huge files your digital camera produces: use an image editing application (or an online tool) to downsize them to the exact pixel width you prefer on the posts and upload these copies instead of the original files. Storage space apart, this will also mean faster loading of your pages, and better quality on the post (because images downsized by WP lose some color and sharpness).

Last question: at the moment i am working with i-pad that gives to the photos I have names like image1, image2, etc.
Then, i upload the photo in wp, and I give it a Title, Description, etc. In my Media Library, but I am not able any more to change the name of file.
Should I change the name of the file, in order to receive more visits (more traffic on my site/blog?), or it's not used? I am not using Urls for most of my photos.

The best image editing application is Photoshop, but it's not free.
Of free alternatives, I'm told that Gimp is good (but I haven't tried it myself).
One online tool could be this:http://www.picresize.com/